1) Field of the Disclosure
The disclosure relates generally to box structures for carrying loads and methods for making the same, and more particularly, to composite bonded box structures for vehicles and architectural structures, and methods of making the same.
2) Description of Related Art
Composite structures, such as carbon fiber-reinforced plastic (CFRP) composite structures, are used in a wide variety of applications, including in the manufacture of aircraft, spacecraft, rotorcraft, automobiles, watercraft, and other vehicles and structures, due to their high strength-to-weight ratios, corrosion resistance, and other favorable properties. For example, in aircraft construction, composite structures are used in increasing quantities to form the wings, tail sections, fuselage, and other components.
Existing composite aircraft transport wing and stabilizer box structures may utilize integrally stiffened panel structures consisting of outer composite wing skin panels, i.e., “skins”, mechanically attached or bonded to an internal wing framework. The internal wing framework may typically consist of reinforcing structures such as spars, ribs, and stringers to improve the strength, stiffness, buckling resistance, and stability of the skins.
Such composite aircraft transport wing and stabilizer box structures are typically fabricated in three separate sections, including the left side outboard wing or stabilizer, the right side outboard wing or stabilizer, and the center section, and such sections are then assembled together. The fabrication process may involve extensive time and manual labor to assemble a large number of component parts, and this may result in increased manufacturing costs. In addition, such sections may be joined together with numerous mechanical fasteners, such as interference fit fasteners, for primary joining purposes. Such fasteners may be made of strong and heavy materials to impart sufficient strength to the sections, hold the sections together during operation of the aircraft, and withstand various aerodynamic loads and stresses. However, the use of numerous heavy fasteners may add weight to the aircraft, which, in turn, may decrease the aircraft's performance and may result in increased fuel required for a given flight profile. This increased fuel requirement may, in turn, result in increased fuel costs. In addition, such fasteners may require additional fuel tight sealing which may increase the fabrication time, labor and cost, and which, in turn, may increase the overall manufacturing and operation costs. Further, the use of numerous fasteners made of metal installed through the outer composite wing skin panels may result in an increased risk of a lightning strike to the wing.
In addition, existing composite aircraft transport wing and stabilizer box structures may typically follow known metal wing box semi-monocoque primary load distribution. As used herein, “semi-monocoque” means a construction approach that supports structural loads by using an object's outer or external skin and stringers, as opposed to using an internal framework that is then covered with a non-load carrying skin. This approach typically requires near traditional 0°/+45°/90° (zero degrees/plus or minus forty-five degrees/ninety degrees) quasi-isotropic (e.g., orientation of fibers in several or more directions in-plane), axially stiffened ply layup orientations that distribute the aircraft transport wing and stabilizer box bending and torsion into both the skins and stringers to provide multiple fail-safe load paths. However, such approach may compromise the efficiency of those composite components and may significantly increase part count in the ribs and fastener attachments in order to maintain stability of the composite aircraft transport wing and stabilizer box structure.
Accordingly, there is a need in the art for improved composite bonded box structures and methods of making the same that provide advantages over known structures and methods.